These countries trade with each other in a common market, meaning that goods can be sold and bought freely across the union. People can also live and work (with some restrictions) in any EU country if they are an EU citizen. Member countries also have some common laws derived from decisions made by the union. Each country in the EU also elects politicians to a European Parliament which helps make and decide what common goals the union should pursue. Fifteen countries in the European Union also share a common currency: the Euro.

Seventeen of the twenty-seven EU member countries use the euro as their currency: France, Germany, Italy, Netherlands, Belgium, Luxembourg, Ireland, Greece, Spain, Portugal, Austria, Finland, Slovenia, Cyprus, Malta, Slovakia, Estonia and Latvia. All other members (except the United Kingdom and Denmark) are obliged by the 1992 Maastricht Treaty to adopt the euro at some point in the future.

In addition, a few smaller countries which are not part of the EU also use the euro: the Vatican City, San Marino, Monaco, Andorra, Montenegro, and Kosovo, a former province of Serbia recognised as independent by most (24 out of 28) EU members, but not by Serbia and many other countries.

The Schengen Agreement was signed by many countries in Europe (including some which are not part of the EU). Countries which have singed up to this agreement have no border controls between similar countries. This means that you can travel from Portugal to Spain to France to Germany to Poland to Lithuania to Latvia to Estonia and Finland (several thousand kilometres) and you don't need to stop at borders, show passports.

The following countries have singed the agreement and removed border controls: Portugal, Spain, France, Luxembourg, Belgium, Netherlands, Germany, Denmark, Iceland (not part of the EU), Sweden, Norway (not part of the EU), Finland, Estonia, Latvia, Lithuania, Poland, Slovakia, Czech Republic, Austria, Switzerland (not part of the EU), Italy, Malta, Slovenia, Hungary, and Greece. Liechtenstein joined at the end of 2011. The only EU countries where passports are still needed to enter from other EU countries are the United Kingdom, Ireland, Cyprus, Romania and Bulgaria. The UK and Ireland (as well as the UK dependencies of Jersey, Guernsey, and the Isle of Man) form the Common Travel Area, which is similar to the Schengen Area in that there are very few border controls between the two countries.